The research paper published by IJSER journal is about Studies on Biodegradability and Mechanical Properties of High Density Polyethylene/Corncob Flour Based Composites 1
ISSN 2229-5518
Corresponding author: Obasi, H.C., neduobasi35@yahoo.com; Tel: +2348039478014
In this study, corncob flour obtained from a waste product of corn threshing processing was blended with high density polyethylene via melt extrusion to produce HDPE/Corncob biodegradable composites. Plastics composites filled with corncob flour are materials that offer a credible alternative for using this botanical resource considering the production of low dense materials with some specific properties. The composite sample showed a decrease in tensile strength and elongation at break and an increase in Young’s Modulus as the filler content increases. PE graft- maleic anhydride (PE-g-MA) was added as a coupling agent. The presence of PE-g-MA gave rise to better properties for modified corncob flour composite (HDPE/CCF1) than the unmodified corncob flour composite (HDPE/CCF) indicating better dispersion and homogeneity of corncob flour to the PE-g-MA matrix. High water absorption resistance and low biodegradation rate of HDPE/ CCF1 as compared with HDPE/CCF showed the effect of coupling agent on the composite. However, water absorption and weight loss of composites buried in soil indicated that both were biodegradable, even at high levels of corncob flour substitution.
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The research paper published by IJSER journal is about Studies on Biodegradability and Mechanical Properties of High Density Polyethylene/Corncob Flour Based Composites 2
ISSN 2229-5518
Synthetic polymeric materials have been extensively used globally due to their excellent chemical, physical and mechanical properties. These properties on the other hand have made them very resistant to microorganisms and other natural degradation forces, so they remain in the environment after disposal. This had led to environmental problems and also in addition to the land shortage problems for solid waste management [1]. Almost everywhere, plastic waste can be seen thereby creating increased costs on the collection and disposal of solid municipal wastes.
Recycling is seen as an attractive and alternative approach to solve this waste problem. However, not all plastics are recyclable and most end up in municipal burial sites. The production and use of biodegradable polymers are considered as possible route to produce the dependence on landfills in solving solid waste problems.
Many attempts have been made on the compounding of petroleum based polymers with natural biopolymers such as cellulose, starch, lignin, chitin and chitosan to produce new products with improved properties and as a way to accelerate polymer biodegradation [2], [3], [4], [5], [6], [7]. These natural biopolymers are abundant, cheap, renewable and completely biodegradable. Using natural biopolymers as fillers to reinforce the composite materials offers the following benefits when compared with mineral fillers [8], [9]: light weight, strong and rigid, environmentally friendly, economical, renewable and abundant resource. On the contrary, the demerits of the materials are [10]: degradation by
moisture, poor surface adhesion to hydrophobic polymers, non-uniform filler sizes, not suitable for high temperature application and its susceptibility to fungal and insect attack.
Biocomposites consist of a polymer (degradable or non-degradable) which is a matrix polymer and cellulose material which act as the reinforcing filler. However, blends of biopolymer and polymer in addition to being susceptible to water absorption exhibit inferior mechanical properties because the hydrophilic character of the biopolymer leads to poor adhesion with the hydrophobic polymer.
There have been many studies on the use of biofillers as reinforcers in biodegradable polymer biocomposite systems. These reinforcing materials can be naturally degraded by microorganisms and play a major role in degrading natural organic substances in the ecosystem [11], [12]. We have studied the application of corncob flour (CCF) as reinforcing filler in the biocomposites. Corncob flour (CCF) is an abundant waste product obtained from the woody core of a maize ear that has limited industrial applications. The use of CCF as reinforcing material for biocomposite can represent the conversion to industrially useful biomass energy [13].
The purpose of this study was to produce composites of high density polyethylene (HDPE) and corncob flour (CCF). However, properties of HDPE become significantly worse when blended with biofiller due to the poor compatibility between the two phases. This condition requires a compatibilizer and/or a coupling agent to enhance the
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The research paper published by IJSER journal is about Studies on Biodegradability and Mechanical Properties of High Density Polyethylene/Corncob Flour Based Composites 3
ISSN 2229-5518
compatibility between the two immiscible phases and to improve the mechanical properties of the composites. In this present study, the incorporation of additive in the corncob based HDPE composites has been considered as a means of improving the mechanical properties and biodegradability of plastic materials made from these blends.
In this regard, the effect of filler loading and maleic anhydride as a coupling agent on the mechanical properties and biodegradability of corncob filler/HDPE blend has been investigated.
The high density polyethylene (HDPE) matrix used in this study was supplied by Ceeplast Industry Ltd, Aba, Nigeria. It is a product of Indorama Group, a subsidiary of Eleme Petrochemical Company Ltd Nigeria with a density of 0.965g/cm3 and a melt flow index (MFI) of 16g/10 min. Polyethylene graft maleic anhydride (PE-g- MA) was obtained from Sigma-Aldrich
chemical corporation. The bio-flour used as the reinforcing filler was corncob flour (CCF) was obtained from Agro-produce market, Aba as woody core of maize ear and then processed to obtain corncob flour. The CCF mesh size used was 300mm.
The CCF was melt-blended with HDPE in an extruder. The filler was first oven dried as 90˚C for 24 h to adjust its moisture content and then stored in a polyethylene. A laboratory size extruder Haake Rheomex CTW 100p was used for compounding
corncob flour and high density PE. The screw speed was 50 rpm and the temperature range varied from 150 to 170˚C. CCF loadings were from 40, 45, 50, 55 and 60 wt. (%). PE-g-MA was used at an amount of 2 wt (%) based on the weight of filler. The hot press process involved preheating at 170˚C for 10 min followed by compression at the same temperature for 4minutes. After this, the sample was allowed to cool down at ambient temperature and the samples were carefully removed from the moulds.
Tensile tests were carried out using a universal Instron tensile tester 3366 according to ASTM D 638 with the samples obtained as described. Tensile properties were measured at room temperature at
5mm/min crosshead speed to obtain the tensile strength, elongation at break and Young’s modulus.
The water absorption tests were conducted for the various sample specimens. Each sample was weighed prior to immersion in distilled water. Weight gains were recorded by periodic removal of the specimens from the water. Moisture on the surface of the sample was removed with filter paper, re- weighed and the percentage water absorption calculated. Results were recorded every 1 week for 9 weeks. The percentage water absorption was calculated according to the equation:
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The research paper published by IJSER journal is about Studies on Biodegradability and Mechanical Properties of High Density Polyethylene/Corncob Flour Based Composites 4
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Where, W0 and W1 are the weights of dried sample and the sample after exposure to water absorption respectively.
Biodegradation of the samples was studied by the soil burial test method. Blend samples with 3.0 x 3.0 x 1.5 mm dimensions were dried and weighed to obtain a dry weight. These samples were then buried in the test soil at depth of 15 cm from the surface for 9 weeks. After 1-week, the samples were carefully washed with water and dried to obtain a new weight. The percentage weight loss was calculated using the equation:
Where, W2 and W3 are the weights of dried sample before and after burial in the soil.
Mechanical properties are great significance for all bio-filled polymer composites applications. Figs 1-3 show the effect of filler loading on tensile strength, elongation at break and Young’s modulus for HDPE/CCF1 and HDPE/CCF composites. We observed that the tensile strength for HDPE/CCF decreased continuously with increasing filler loading (Fig. 1). It was thus clear that the mechanical incompatibility of the two phases was great and would increase with the filler content. This behavior has been described in similar studies and has been explained by the increase of the interfacial area with filler loading [14], [15].
Though lower tensile strength at break was observed for HDPE/CCF1 composites compared with neat HDPE, this decrease was smaller than that of the HDPE/CCF composites. The absolute value of tensile strength for all compatibilized HDPE/CCF1 composites was higher than that of uncompatibilized HDPE/CCF composites. This behaviour could be attributed to the reaction of the hydrophilic –OH groups from the filler and the acid anhydride groups from PE-g-MA, thus forming ester linkage, as established in the literature works [16]. The reaction fosters strong adhesion between filler and matrix interface creating thus a better stress transfer from the matrix to the filler leading to higher tensile strength [17]. Simple adhesion of the polymer to the filler through weak bonding or induction interactions is experienced in the absence of chemical modification.
Incorporation of the filler resulted in a decrease in elongation at break. Fig. 2 shows the effect of filler loading on the elongation at break of HDPE/CCF1 and HDPE/CCF composites. We observed that the elongation at break for the composites decreases with increasing filler loading. The reduction of the elongation at break with the increasing filler loading indicates the inability of the filler to support the stress transfer from polymer matrix to filler. It can be seen that the elongation at break for HDPE/CCF1 is lower than for HDPE/CCF. These observations were in agreement with the results presented by researchers [18], [19]. However, the effect of the compatibilizer was not evident on this property.
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The research paper published by IJSER journal is about Studies on Biodegradability and Mechanical Properties of High Density Polyethylene/Corncob Flour Based Composites 5
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Results obtained from Young’s modulus determination indicated that increasing filler loading showed a tendency to increase the composite stiffness for HDPE/CCF1 and HDPE/CCF composites (Fig.3).
The increase in modulus was observed because as starch content is increased, filler- filler interaction becomes more pronounced than filler-matrix interaction. Again, the increased modulus corresponds to more filler where its intrinsic properties as a request agent exhibit high stiffness compared to polymeric material [20]. This is in agreement with the result reported by Ardhyananta et al [21]. Some researchers have also related the increase in composites rigidity with the reduction in polymer chains mobility in the presence of the filler [22].
The Young’s modulus for HDPE/CCF1 with the addition of compatibilizer showed a higher modulus than the uncompatibilized HDPE/CCF. This result might be due to the compatibilizing effect of the PE-g-MA in the composites which enhanced high interfacial interaction between the fillers and PE matrix in which the fillers strengthen the composite materials.
The effects of corncob flour on water absorption of the blends for the compatibilized HDPE/CCF1 and uncompatibilized HDPE/CCF composites after immersion in water for 1-week interval of time for 9 weeks are shown in figs. 4 and
5. From the figures, water absorption for both compatibilized and uncompatibilized composites increased with the increase in corncob loading. This is due to the
hydrophilic nature of the corncob flour by virtue of the presence of an abundant hydroxyl groups which are available for interaction with molecules. Again, as the filler loading increases, agglomerate formation increases thus creating difficulties in achieving a homogenous dispersion of filler in the composite. This results in water molecules penetration into the composites through voids created by agglomeration which increases water absorption of the composites [23], [24].
The figures showed lower percentage of water absorption by HDPE/CCF1 as compared to the HDPE/CCF composites. The compatibilized HDPE/CCF1 composite has better adhesion between the matrix and the filler, reducing the formation of agglomerates. Thus modification of the corncob flour led to the decrease in the number of free hydroxyl groups on the surface, reducing the percentage of water absorption.
The biodegradability of corncob flour blended with HDPE was estimated using soil burial test method. Figs. 6 and 7 show changes in weight ratio (initial sample/buried sample) with time for the HDPE/CCF1 and HDPE/CCF buried in the soil. In the soil, water diffuses into the composite sample, causing swelling and enhancing biodegradation. The weight loss of the sample after burial in the soil for 9 weeks was determined. The weight was observed at each time point over the period of study was larger with increasing starch content in the composite. This means that percent weight loss of both compatibilized
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The research paper published by IJSER journal is about Studies on Biodegradability and Mechanical Properties of High Density Polyethylene/Corncob Flour Based Composites 6
ISSN 2229-5518
and uncompatibilized composite increases continuously with increase in the number of weeks indicating that the samples continuously degrade with increase in the length of time and suggested that microorganisms consume starch and create pores in the PE matrix. However, HDPE/CCF1 had a lower weight loss ratio than the HDPE/CCF. The higher biodegradation of HDPE/CCF may be caused by the same factors leading to its higher water absorption and lower mechanical properties.
Woody core of a maize ear was milled, dried and used as filler in HDPE composite. It was observed that it is plausible to use this waste product of the maize grain cob as low cost filler, in view of the properties obtained from the products. The composites stiffness was seen to increase with increasing filler loading. Though tensile strength decreased slightly, they were improved in the presence of the coupling agent PE-g-MA due to the formation of an ester linkage not present in HDPE/CCF. This account for the differences in properties and behaviour showed by the two composite materials.
Both HDPE/CCF1 and HDPE/CCF demonstrated increase in water absorption and weight loss with increase in starch content. High water resistance and low biodegradation loss rate of HDPE/CCF1, however, were observed when compared with HDPE/CCF composites.
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FIGURES
18
16
14
12
10
8
6
4
2
0
0 40 45 50 55 60
HDPE HDPE/CCF1
HDPE/CCF
Fig 1: Effect of filler loading on the tensile strength of CCF-filled HDPE composites
16
14
12
10
8
6
4
2
0
0 40 45 50 55 60
HDPE HDPE/CCF1
HDPE/CCF
Fig 2: Effect of filler loading on the elongation at break of CCF-filled HDPE composites
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155
150
145
140
135
130
125
120
115
110
0 40 45 50 55 60
HDPE
HDPE/CCF1
HDPE/CCF
Fig 3: Effect of filler loading on the Young’s modulus of CCF-filled HDPE composites
16
HDPE
14 HDPE/40 CCF1
HDPE/45 CCF1
12 HDPE/50 CCF1
HDPE/55 CCF1
10
HDPE/60 CCF1
8
6
4
2
0
1 2 3 4 5 6 7 8 9
Fig 4: Water absorption versus time of HDPE/CCF1 at different filler loadings
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International Journal of Scientific & Engineering Research Volume 3, Issue 8, August-2012 11
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25
HDPE
20 HDPE/40 CCF
HDPE/45 CCF
HDPE/50 CCF
HDPE/55 CCF
HDPE/60 CCF
5
0
1 2 3 4 5 6 7 8 9
Fig 5: Water absorption versus time of HDPE/CCF at different filler loadings
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20
18 HDPE
16 HDPE/40 CCF1
14 HDPE/45 CCF1
HDPE/50 CCF1
HDPE/55 CCF1
HDPE/60 CCF1
6
4
2
0
1 2 3 4 5 6 7 8 9
Fig 6: Weight loss versus time of HDPE/CCF1 at different filler loadings
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25
HDPE
20 HDPE/40 CCF HDPE/45 CCF
15 HDPE/50 CCF HDPE/55 CCF
HDPE/60 CCF
5
0
1 2 3 4 5 6 7 8 9
Fig 7: Weight loss versus time of HDPE/CCF at different filler loadings
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